Cerebrovascular dysfunction in diabetes mellitus may be related to alterations in cellular pathways to increase oxidative stress and thus impair nitric oxide synthase (NOS)-dependent reactivity of cerebral vessels. However, cellular/molecular mechanisms by which oxidative stress contributes to cerebrovascular dysfunction remain unknown. We suggest that diabetes impairs reactivity of cerebral vessels by mechanisms that alter several key cellular systems (renin-angiotensin system, protein kinase C, NAD(P)H oxidase, superoxide dismutases and/or endothelial nitric oxide synthase). Alterations in these important enzyme pathways ultimately lead to an increased formation of superoxide anion that can inactivate nitric oxide. Thus, the central hypothesis of this application is that mechanisms contributing to cerebral oxidative stress in diabetes, with consequent effects on nitric oxide bioavailability, lead to impaired reactivity of cerebral vessels. We propose the following specific aims. In specific aim #1, we will test the hypothesis that angiotensin II- dependent activation of NAD(P(H oxidase increases superoxide anion production by cerebral vessels and contributes to cerebrovascular dysfunction in diabetes. In specific aim #2, we will test the hypothesis that diabetes may produce cerebrovascular dysfunction by stimulating superoxide anion production via a protein kinase C-dependent activation of NAD(P)H oxidase. In specific aim #3 we will test the hypothesis that impaired NOS-dependent dilatation of cerebral vessels in diabetic animals may be explained by an uncoupling of eNOS via a reduced availability/utilization of tetrahydrobiopterin (BH4). Finally, in specific aim #-4, we will test the hypothesis that alterations/manipulationns in superoxide dismutases can account for and prevent impaired responses of cerebral vessels in diabetes. We will use state-of-the-art in vivo methodologies coupled with innovative biochemical/molecular/genetic approaches to investigate mechanisms that underlie endothelial dysfunction of cerebral vessels in diabetes. We suggest that our results will provide novel insights regarding therapeutic approaches for the treatment/prevention of cerebrovascular dysfunction in diabetes.